LONDON (AFP) - Prince William and his wife Kate thanked well-wishers on Thursday ahead of the birth of their second child expected this month, with royal sources saying it will be in the same hospital as their first.

Kate will return to the Lindo Wing, the private maternity department of St Mary's Hospital in Paddington in central London where third in line to the throne Prince George was born in 2013.

The hospital charges more than £5,000 (S$10,000) for the first 24 hours of a delivery with an extra £1,000 for each additional night.

"The Duke and Duchess are hugely grateful for the warm wishes they have received from people throughout the UK and indeed around the world and over the last few months," a royal source told British media, using the couple's official title, the Duke and Duchess of Cambridge.

"They know that people are excited that Prince George will soon have a little brother or sister, it means a great deal to them that so many will be celebrating this important moment for their family."

Sources said that the couple still do not know if the baby will be a boy or a girl and that the delivery team will be led by Guy Thorpe-Beeston, surgeon gynaecologist to the Royal Household.

William will take two weeks of paternity leave from the training he is receiving for his new job as an air ambulance helicopter pilot.

He and Kate are planning to spend the first few days after the birth at their London residence, Kensington Palace, before travelling to Anmer Hall in Norfolk, a mansion on Queen Elizabeth II's Sandringham estate where they have set up home.

The birth will be announced both on the official Kensington Palace Twitter account and in the traditional way - with a royal bulletin displayed on an ornate easel in Buckingham Palace's forecourt.